Activate Perilous Forays by paying ({1} magic symbol) and sacrificing a creature, searching your library for a land with a basic land type and putting it onto the battlefield tapped.
The land enters the battlefield, triggering Sporemound and Nissa.
Resolve the Nissa trigger, adding ({1} magic symbol) .
Resolve the Sporemound trigger, creating a 1/1 Saproling creature token.
Repeat.
Results
Near-infinite death triggers.
Near-infinite ETB.
Near-infinite landfall triggers.
Near-infinite LTB.
Near-infinite sacrifice triggers.
Put all lands with a basic land type from your library onto the battlefield tapped.